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861.
The column-switching technique has been widely used to determine trace level ions in the presence of high concentration matrix.
A novel simplified column-switching method is proposed where bromate (as a model compound) was determined using this technique.
The switching time window was confirmed by the retention time of determined ions. This technique can completely carry out
the same function as the other column-switching technique do, but only one extra ten-way injection valve coupled to ion chromatograph
was used. By using column-switching technique, it is possible to determine 0.2 μg L−1 bromate in the presence of 100 mg L−1 chloride by direct injection of 2000 μL without any pretreatment and the relative standard deviation (RSD) of the peak height
for the eleven successive injections of 0.2 μg L−1 bromate solution is 23.1%. The detection limit for bromate is 0.09 μg L−1, which showed the method was very sensitive. The technique has been applied to the determination of bromate in drinking water,
and the spike recovery is in the range of 96–104%. 相似文献
862.
In April 1998 Raimond Castaing left the world of electrons, of ions and others particles, his wife and his family, his numerous
students, for the world of stars.
Raimond Castaing (Fig. 1) had a very strong personality. No one will forget their first meeting with him and all his students
remember how brilliant he was as a teacher. A lot of anecdotes about his famous hot temper are still circulating among his
friends and his former students. But in this paper, we would like to evoke Castaing’s memory through his achievements in Instrumental
Physics, from the time of his doctoral thesis to later developments with his students, which were all centred on the imaging
of the microstructures of materials and their quantitative chemical analysis. 相似文献
863.
A very simple, highly sensitive and selective chemiluminescence (CL) method was established for the determination of cysteine. This method is based on the fact that the CL reaction of luminol and hydrogen peroxide can be greatly enhanced by cysteine. The CL intensities at maximum light emission were linearly correlated with the concentration of cysteine over the range of 2.0×10–8–6.0×10–6molL–1 with a detection limit of 7.5×10–9molL–1. The relative standard deviation was 1.7% for the determination of 1.0×10–7molL–1 cysteine (n=9). The feasibility of utilizing the proposed method for the determination of total concentration of cysteine in human serum was examined. 相似文献
864.
T. V. Mitkina D. Yu. Naumov O. A. Gerasko F. M. Dolgushin C. Vicent R Llusar M. N. Sokolov V. P. Fedin 《Russian Chemical Bulletin》2004,53(11):2519-2524
The inclusion compound of macrocyclic cavitand cucurbit[8]uril (CB[8]) with the nickel(II) complex containing the tetraazamacrocyclic ligand cyclam, {[Ni(cyclam)]@CB[8]}Cl2··16H2O (1), and the inclusion compounds of CB[8] with the copper(II) bis-ethylene-diamine complex, {trans-[Cu(en)2(H2O)2]@CB[8]}Cl2·{CB[8]}·42H2O (2a) and {trans-[Cu(en)2(H2O)2]@CB[8]}Cl2·17H2O (2b), were synthesized and characterized by X-ray diffraction analysis, IR and ESR spectroscopy, and electrospray mass spectrometry. Guest—host inclusion compounds can be directly synthesized starting from a metal complex and cucurbit[8]uril, as was exemplified by the preparation of compounds 2a and 2b.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2414–2419, November, 2004. 相似文献
865.
A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. The procedure is based on the effect of oxalate on the oxidation of Victoria blue B by dichromate in dilute sulfuric acid medium. The reaction is quantitatively estimated by measuring the decrease in absorbance of Victoria blue B at the maximum wavelength of 610nm after quenching the reaction with tap water. The factors effecting the sensitivity and reproducibility of the reaction were studied. The method is not interfered with by foreign species generally associated with oxalate and oxalic acid. The described method is simple, specific, inexpensive and suitable for oxalic acid concentrations of between 0.06 and 9.0µgmL–1. It was validated with satisfactory results by determining oxalic acid content in water extracts from plant materials such as spinach and Lathyrus sativus. 相似文献
866.
Pablo A. Molina R. Steven Sikorski Jan H. Jensen 《Theoretical chemistry accounts》2003,109(3):100-107
The relationship between hydrogen bonding and NMR chemical shifts in the catalytic triad of low-pH α-chymotrypsin is investigated
by combined use of the effective fragment potential [(2001) J Phys Chem A 105:293] and ONIOM–NMR [(2000) Chem Phys Lett 317:589] methods. Our study shows that while the His57 Nδ1−H bond is stretched by a relatively modest amount (to about 1.060 ?) this lengthening, combined with the polarization due
to the molecular environment, is sufficient to explain the experimentally observed chemical shifts of 18.2 ppm. Furthermore,
the unusual down-field shift of Hɛ1 (9.2 ppm) observed experimentally is reproduced and shown to be induced by interactions with the C=O group of Ser214 as previously
postulated. The free-energy cost of moving Hδ1 from His57 to Asp102 is predicted to be 5.5 kcal/mol.
Received: 26 September 2001 / Accepted: 6 September 2002 / Published online: 21 January 2003
Contribution to the Proceedings of the Symposium on Combined QM/MM Methods at the 222nd National Meeting of the American
Chemical Society, 2001
Correspondence to: J. H. Jensen e-mail: jan-jensen@uiowa.edu
Acknowledgements. This work was supported by a Research Innovation Award from the Research Corporation and a type G starter grant from the
Petroleum Research Fund. The calculations were performed on IBM RS/6000 workstations obtained through a CRIF grant from the
NSF (CHE-9974502) and on supercomputers at the National Center for Supercomputer Applications at Urbana-Champaign. The authors
are indebted to Visvaldas Kairys for help with the CHARMM program, and to Daniel Quinn for many helpful discussions. 相似文献
867.
Shigeo Minami 《Mikrochimica acta》1987,93(1-6):309-324
Multichannel Fourier transform spectrometers utilizing image sensing devices are reviewed along with the instrumental design concepts. Although the idea itself is fairly simple, a photographic plate in holographic spectroscopy is replaced by an image sensor, there are stringent requirements to be satisfied in order to realize the system for field use. Mainly two types of the instrument, which are characterized by the Sagnac common-path interferometer and the polarization interferometer optics, respectively, are described with regard to their system performances. Examples of the system operation introduced show that Fourier transform spectrometers without mechanical moving parts play an important role in a variety of spectroscopic applications under severe surroundings. In a summary, methods for the resolution enhancement and comments on the signal-to-noise ratio are also included. 相似文献
868.
With the accelerated accumulation of genomic sequence data, there is a pressing need to develop computational methods and advanced bioinformatics infrastructure for reliable and large-scale protein annotation and biological knowledge discovery. The Protein Information Resource (PIR) provides an integrated public resource of protein informatics to support genomic and proteomic research. PIR produces the Protein Sequence Database of functionally annotated protein sequences. The annotation problems are addressed by a classification-driven and rule-based method with evidence attribution, coupled with an integrated knowledge base system being developed. The approach allows sensitive identification, consistent and rich annotation, and systematic detection of annotation errors, as well as distinction of experimentally verified and computationally predicted features. The knowledge base consists of two new databases, sequence analysis tools, and graphical interfaces. PIR-NREF, a non-redundant reference database, provides a timely and comprehensive collection of all protein sequences, totaling more than 1,000,000 entries. iProClass, an integrated database of protein family, function, and structure information, provides extensive value-added features for about 830,000 proteins with rich links to over 50 molecular databases. This paper describes our approach to protein functional annotation with case studies and examines common identification errors. It also illustrates that data integration in PIR supports exploration of protein relationships and may reveal protein functional associations beyond sequence homology. 相似文献
869.
The acid dissociation constants of 1,2-bis(cis-aminophenoxy)ethane-N,N,N′,N′;-tetraacetic acid (H4BAPAT or H4Z), and the stability constants of its chelates with tripositive rare-earth metal ions have been determined by the potentiometric titration and mercury indicator electrode methods at 15°, 25′ and 35°C and an ionic strength of 0.1 (KNO3). The existence of a monohydrogen chelate species, LnHZ, and the normal chelate, LnZ?, is illustrated. Enthalpy and entropy changes characterizing the formation of the normal chelates and the dissociation of the last two protons of chelating acid have been calculated at 25°C. These functions have been compared with corresponding values for related chelating agents. 相似文献
870.
The ground state of the van der Waals-type lanthanide dimer Yb2 has been studied by means of relativistic energy-consistent ab initio pseudopotentials using three different core definitions.
Electron correlation was treated by coupled-cluster theory, whereby core-valence correlation effects have been accounted for
either explicitly by correlating the energetically highest coreorbitals or implicitly by means of an effective core-polarization
potential. Results for the first and second atomic ionization potentials, the atomic dipole polarizability, and the spectroscopic
constants of the molecular ground state are reported. Low-lying excited states have been investigated with spin-orbit configuration
interaction calculations. It is also demonstrated for the whole lanthanide series that correlation effects due to the atomic-like,
possibly open 4f-shell in lanthanides can be modeled effectively by adding a core-polarization potential to pseudopotentials attributing the
4f-shell to the core.
Received: 3 April 1998 / Accepted: 27 July 1998 / Published online: 9 October 1998 相似文献